Aliphatic polyesters have drawn attention as biodegradable plastics, which can be easily degraded in nature, and as “green” plastics, which can be synthesized from renewable carbon resources such as sugar or vegetable oil. At present, for example, a polylactic acid having a polylactic acid backbone has been put to practical use as an aliphatic polyester.
An example of a known technique for producing an aliphatic polyester such as polylactic acid with the use of recombinant microorganisms is disclosed in Patent Document 1 (WO 2006/126796). Patent Document 1 discloses a recombinant E. coli cell resulting from introduction of a gene encoding an enzyme converting a lactic acid into lactyl-CoA and a gene encoding an enzyme synthesizing polyhydroxyalkanoic acid using lactyl-CoA as a substrate into a host E. coli cell. The technique disclosed by Patent Document 1 involves the use of the pct gene derived from Clostridium propionicum as a gene encoding an enzyme converting a lactic acid into lactyl-CoA. In this technique, the phaC2 gene derived from the Pseudomonas sp. 61-3 strain is used as a gene encoding an enzyme synthesizing polyhydroxyalkanoic acid using lactyl-CoA as a substrate.
However, the technique of Patent Document 1 is insufficient in terms of the productivity of aliphatic polyesters, such as polylactic acids, and various attempts made aimed at improving such productivity have been insufficient. For example, Patent Document 2 (WO 2008/062999) discloses an attempt to enhance the capacity to synthesize a lactic acid homopolymer or polylactic acid copolymer using lactide-CoA as a substrate via introduction of a given mutation into the phaC1 gene derived from the Pseudomonas sp. 6-19 strain. In addition, Patent Document 3 (WO 2009/131186) discloses a technique for producing a polymer comprising 3-hydroxybutyric acid and lactic acid by introducing a given mutation into the phaC1 gene derived from the Pseudomonas sp. 61-3 strain to cause mutations in amino acids at positions 130, 325, 477, and 481.